Congenital muscular dystrophies: weakness present from birth or infancy

Congenital in this context describes timing, not cause. A baby may be unusually floppy at birth, slow to hold their head up or achieve sitting, or have joints that are fixed in position at birth. Some children never walk independently, whereas others walk with support or even without it.

The group is defined by features seen on muscle biopsy, which show dystrophic changes with scarring and fibre degeneration, together with the early onset. Over time, advances in genetics have split the group into many separate named conditions based on which protein is missing or abnormal.

The proteins affected include structural components outside the muscle fibre, proteins that glycosylate (add sugar chains to) structural proteins, and components of the nuclear envelope and the sarcomere. The clinical consequences differ.

• Collagen VI-related: a spectrum from mild Bethlem muscular dystrophy to severe Ullrich congenital muscular dystrophy, with joint contractures and sometimes breathing difficulty; most cases are autosomal dominant, according to MedlinePlus.

• Laminin alpha-2 (LAMA2, sometimes called merosin deficiency): weakness from infancy, often with brain white matter changes on MRI and normal intelligence in many children.

• Alpha-dystroglycanopathies: a large group in which brain and eye development may be affected, in addition to muscle.

• LMNA-related congenital muscular dystrophy: early head drop and neck weakness, with a risk of respiratory failure.

• SEPN1-related and others: sometimes classified separately as rigid spine syndromes with early respiratory weakness.

Assessment of a floppy infant is carried out by paediatric neurology and neuromuscular teams. Creatine kinase may be raised or normal depending on the type, and MRI of the brain and muscle can show patterns that point to specific genes. The NHS lists genetic screening, blood tests, electromyography, muscle biopsy and MRI as tests used for muscular dystrophy generally.

Whole-genome sequencing or targeted panels, available through the NHS Genomic Medicine Service for seriously ill children with a suspected genetic disorder, have become the usual route. Muscle biopsy with protein staining may still be used if the genetic result is uncertain. NHS genetic testing is free when arranged by a hospital specialist.

Care depends on type but typically includes physiotherapy to protect joint range, orthotics and seating, monitoring of the spine for scoliosis, and respiratory assessment. Where breathing muscles are weak, early overnight breathing support and cough assistance can make a considerable difference. Feeding and swallowing review, nutrition support and, for some children, gastrostomy feeding may be discussed.

The NHS describes supportive treatment for muscular dystrophy including physiotherapy, surgery for complications, respiratory support and occupational therapy. For CMD with heart involvement, cardiac surveillance is added. Where the brain or eyes are affected, developmental support, epilepsy care and ophthalmology are part of the plan.

Outlook depends greatly on the type. Mild forms may allow independent walking and near-normal life expectancy, while severe forms can cause early respiratory failure. A specialist team can give a more individual view after the genetic result is known and the pattern of weakness is observed over time.

Most CMD types are autosomal recessive, so parents are usually healthy carriers with a 1 in 4 chance of another affected child in each pregnancy. Collagen VI conditions are more often dominant and may arise from new mutations. Clinical genetics can explain recurrence risk and options including prenatal diagnosis.